The present invention relates to a rotational speed detecting apparatus for electronically-controlled fuel injection systems which detects the rotational speed of an engine in accordance with engine operating parameters other than the actual engine rotational speed.
In the past, there have been electronically-controlled fuel injection systems for supplying fuel to internal combustion engines, in which the supply of fuel is cut off during the periods of deceleration of the engine, and the fuel is enriched during the periods of starting, high load operation and the like. While these fuel cut-off and fuel enrichment have the advantage of ensuring accurate fuel supply to the engine, both of these operations are effected in relation to the engine rotational speed, thus requiring very complicated means for detecting the engine rotational speed. In other words, it is necessary to provide a rotational speed detector for discriminating the rotational speed ranges and a plurality of comparators each comparing the detected rotational speed with a preset value. This results in an increase in the number of elements used, thus increasing the cost of the apparatus and deteriorating its reliability.